Power cylinder with piston return by own vacuum force

ABSTRACT

A power cylinder converting pressure energy into linear motion and more particularly to a power cylinder having cylinder and piston of differential diameters and designed so as to create vacuum force by the piston forward motion inside a cylinder subjected to pressurized fluid to extend a piston rod attached thereto and to perform work, said vacuum force large enough to return piston and rod assembly back into the original first retracted position without the use of springs and capable of operating as a double acting cylinder controlled by a simple 3way valve of solenoid or manual type.

United States Patent [1 1 Pauliukonis June 11, 1974 [76] Inventor:Richard S. Pauliukonis, 6660 Greenbriar Dr., Cleveland, Ohio 44130 221Filed: Apr. 14, 1972 1211 Appl. NO; 244,019

[521 US. Cl 92/86, 92/130, 92/132, 92/170, 92/248 [51] Int. Cl. FOlb31/00, Fl6j H00 [58] Field of Search 92/86, 107, 130, 132, 152, 92/170,248, 249; 91/469 2,982,257 5/1961 Fagge 92/152 X 3,040,712 6/1962 Harrah92/248 X 3,063,423 11/1962 Riordan l l 92/86 X 3,376,795 4/1968 Allen92/132 X Primary Examinerlrwin C. Cohen [57] ABSTRACT A power cylinderconverting pressure energy into linear motion and more particularly to apower cylinder having cylinder and piston of differential diameters anddesigned so as to create vacuum force by the pisston forward motioninside a cylinder subjected to pressurized fluid to extend a piston rodattached thereto and to perform work, said vacuum force large enough toreturn piston and rod assembly back into the original first retractedposition without the use of springs and capable of operating as a doubleacting cylinder controlled by a simple 3-way valve of solenoid or manualtype.

7 Claims, 2 Drawing Figures POWER CYLINDER WITH PISTON RETURN BY OWNVACUUM FORCE The present invention relates to the fluid power equipment,and more particularly to an actuating power cylinder applicable alike tosingle acting or double acting actuators energized either hydraulicallyor pneumatically in a-given power system, although in its preferredspecific embodiment, it is most efficient in single acting cylinders.

The inherent defects and shortcomings of existing power cylinders of thedouble acting type necessitating the use of 4-way valves for theiroperation, result in premature cylinder deterioration when subjected tounidirectional load service because of the physical abuse the cylinderexperiences upon return with full force of the working fluid affectingthe piston and cylinder end with resultant energy waste and productdeterioration prematurely, in particular if employed with pressurereducers in a conduit less loaded because of reducer inefficiency in theultimate analysis, plus extra cost, extra spacerequirements and systemreliability reduction, all passed over to the user of conventionalsystems at the expense of ignorance and lack of better components.

In single acting-spring return cylinders thatnormally require theme of a3-way directional valve for their operation, the return of the pistonfrom the extended position to that of the retracted position is done bya spring assembled thereto, with the spring resistance representing asizeable energy loss during the spring compression cycle. In addition,the use of a spring requires an extra length of cylinder body for springaccommodation with more waste. Standard diameter piston rods presentlyused with conventional cylinders are limited as to the side loads theytolerate.

Prior art cylinders normally made of metallic cylindrical bodieswithin'which are located all metallicpiston rod assemblies and metallicend caps, including appropriate elastomer seals, and consisting of apiston to which an actuating rod is secured permanently either bysoldering or simply by bolting together, can beconsidered obsolete inview of the proposed improvements this invention offers. it is obviouslydesirable to provide cylinders of simplified design with improvedquality, performance and operating capabilities. It is also desirable toprovide a cylinder which can be mass produced utilizing a process andequipment known to reduce cylinder manufacturing costs. The presentinvention provides a cylinder which incorporates completely new featuresin cylinder design, with differential diameter piston capable of beingmass produced at reduced manufacturing cost. This cylinder even whenproduced by conventional means provides design simplification andimproved service, because of a built in facility to perform as a doubleacting cylinder, while actuated by a simple 3-way directional valve as aresult of a vacuum force, such design further enabling cylinderoperation as either a single acting or as a double acting cylinder.

Further, when operating as a double acting cylinder the pistonrodassembly retracts automatically by its own vacuum force created bythe differential diameter piston inside differential diametercylinderthereby dispensing of a costly 4-way valve conventional double actingcylinders necessitate. When operating as a single acting cylinderactuated by a 3-way valve, the automatic re-traction of piston rodassembly permits dispensing of springs conventional single actingcylinders necessitate. This invention also enables the fabrication of anall-plastic power cylinder with one-piece piston rod assembly at adrastic cost reduction. It further provides a means of molding adifferential diameter piston with a rod of metal, is desired, or forintegrally molding at least one end cap with the differential diametercylinder body from any material, metal or plastics.

The present invention provides cylinders of this general type which aresimple in design because of reduced cylinder complexity, and hencecompetitive in cost. It should be noted that the cylinder according tothe present invention is particularly suitable for miniaturization andautomation, but is by no means limited to it.

These and other objects and advantages of the invention will become morefully apparent from the following description of the embodiment of theinvention. taken together with the accompanying drawings.

IN THE DRAWINGS.

FIG. 1 is a cross-sectional view of a typical power cylinder ofdifferential diameter design with piston rod retracted, and a piston rodassembly fabricated.

FIG. 2 identifying functionally identical cylinder to that of FIG. 1except for position of piston, shows the details of an all plasticcylinder of differential diameter design which are typical to injectionmolded products. with piston rod extended depicting evacuated annulusmore conspicuously.

Shown in FIG. 1 is an all-metal one piece cylinder housing 1, having atubular body 2 of differential internal diameters with a small internaldiameter 3 closed by a blind end 4 which in the illustrated case isintegral with cylinder 3 but in practice may be a detachable cylinderblind end. e

The small diameter cylinder 3 continues longitudinally inwardly towardthe opposite cylinder open receiver end 5 midway initiating with acoaxial larger cylindrical portion 6 which starts at shoulder 24dividing the differential diameter tubular body into one smallerdiameter cylinder 3 provided with a blind end wall 4 and another largerdiameter coaxial cylinder 6 with an open receiver end 5. A fluidentrance port 7 is provided in the cylinder blind end 4 to serve assupply and exhaust port means for pressurized working fluid whenprovided with a 3-way operating valve( not shown An all-metal coaxialpiston and rod assembly 28 holds an elongated differential diameterpiston 8 at one 4 end and a tubular piston rod 9 at the other end.Midway thereof is situated a larger diameter short piston 17 with rod 9secured thereto centrally by means of threads 10 entering face 21 ofpiston 17 while the smaller diameter piston 11 of elongatedconfiguration terminates at piston end 14 facing cylinder blind end wall4 when slidably inserted into the differential diameter body 2. Thediameter of piston 11 is made to be slightly less than that of theinternal diameter 3 to facilitate close sliding fit of the elongatedpiston 11 which is slightly shorter than the portion of the cylinder 3inside tubular body 2 allowing piston 17 to bottom first and to rest onthe shoulder 24 when piston is assembled, with diameter of piston 17approaching that of the larger cylindrical portion6. Grooves l2 and 13housing seals 15 and 16 respectively are located at the piston end 14 ofthe small diameter piston 11 facing cylinder blind end wall 4. A seal 18permanently secured inside larger diameter piston 17 insures that thespace between seals 16 and 18 is never exposed to the working fluidunder pressure entering the fluid entrance port 7 in blind end wall 4,and is not open to the atmosphere during the cycling of the piston-rodassembly in operation irrespective of the position of the piston insidethe cylinder. This is so because seal 16 never disengages small diametercylinder 3 even if piston-rod assembly is; in the extended position asthat shown in FIG. 2,and the seal 18 inside piston 17 never leaveslarger diameter cylindrical portion 6 when the cylinder is operated withpiston-rod assembly moving axially from piston rod retracted firstposition shown in FIG. I to that of piston-rod extended second positionshown in FIG. 2. I

Between the seal grooves 12 and 13 there is a small hole 19 radiallyentering piston end 14 to lead toward a blind axial bore 20 beginning atthe center of large piston face 2l'partially threaded inwardly as shownby 22 to receive tubular piston rod 9 provided with mating threads 10,and exhausting to the atmosphere, should seal 15 exposed to the workingfluid pressure leak, and to insure that no air lock between seals 15 and16 hinders cylinder operation, as well as to permit air ventingduring'the initial piston assembly with smaller cylinder while changingposition is doing work and simultaneously creating a new annulus atvacuum between 3 while forcing large piston to expel all air from thespace it accupies' when bottomed initially against the shoulder 24 andto displace such air between seals 16 and 18 when piston 11' ispositioned in the cylinder as shown in FIG. 1. Experiments with,different se'alconfigurations in piston grooves-identified a need fordifferentte chniques to force'piston against the shoulder24-initially'in order to insure a complete air displacement from thespace to be filled by the differential diameter piston 8 when pistonrodis in the first retracted position, and ,to' render completely evacuatedannulus between piston 11 and cylindrical portion 6 when piston rodis'in the second extended position. It was found howeverfthat afterinitialpiston assembly with the differential diameter cylinder, theoperation of the cylinder is not dependent on seal configuration at allalthough the use ofU -cups has facilitated considerably easier cylinderassembly initially and could be used succesfully in lieu of O-rings forcylinder sealing during cylinder operation in service. In theillustrated case of FIG. 1, the large di'ameter piston 17 againstshoulder 24 identifies piston rod position after initial assembly of thecylinder. -A rod end closure 26 provided with central opening 27 for thepassage of rod.9 during the position change of the piston-rod assemblyin service, is slipped over'the piston rod 9 and subsequently secured inthe receiver open end 5 permanently serving as a stop that defines'the'cylinder stroke length, to complete cylinder assembly. The centralopening 27 slidably receiving piston rod 9 provides atmospheric rodclearance 27-a around the piston rod 9 to serve as a bearing means inservice, resulting in improved capability for power cylinder to sustainside loads. Opening 27 also provides atmospheric environment for theface 21 of short piston with rod 9. When port 7 is connected to thepressurized working fluid controlled by a 3-way valve, the smallcylinder end 29 may be energized. The working fluid entering port 7pushes against piston end 14 resulting in a position change of thepiston-rod assembly and rod extension at the opposite cylinder end withannulus 2S exhausting via clearance 27-a to the atmosphere. The pistonrod assembly under pressure larger diameter cylindrical portion 6,shoulder 24, piston 17 and the elongated small piston diameter 11between seals 16 and 18 of the'small and large piston ends respectivelyuntil large piston face 21 becomes stopped at the end of piston strokeby inside face 30 of the rod end closure 26 constituting the piston-rodassembly in extended position(shown if FIG. 2) and creating-an evacuatedannular space between seals 16 and 18 as well as shoulder 24 and piston17 facing it. Subsequent rod retraction and return of the piston to theoriginal position shown in FIG. 1 is accomplished automatically by thevacuum force described and in conjuction with atmospheric pressure forceover piston [7 face 21. A simple but effective means of piston rodretraction by its own vacuum'force in accordance with inventionobjectives is hereby provide. Tests with prototypes proved this out.

It should be noted that even with the rod extended there is considerablymore engagement of piston and rod in this cylinder than in conventionalcylinders. This is due to the elongated piston 8 inside tubular body 2having reaction points at pistonsll and 17 wide spread and offering aconsiderably wider bearing span for supporting side loads and therebyincreasing usefulness of such cylinders manyfold. In particular that inthe design of FIG. 1 there is no need for rod seal inside rod endclosure 26, and thus there is no practical limit to the sizedimensionally chosen for the piston rod, a factor limiting the designflexibility of theconventional cylin-, drs which require rod sealsinside the rod end closure.

The net vacuum force together with atmospheric pressure force shall beproportioned so as to enable the return of the piston to the originalposition automatically, and the large piston diameter has to-be sized soas to result in such net vacuum force as needed for proper cylinderoperation in service be it single acting or double actingcylinder withpiston rod return to the original position by its ownvacuum force.

FIG. 2 identifies a cylinder which functionally is identical to thatshown in FIG. 1 except for modifications in both materials ofconstruction and means ofsealing during the piston axial motion withinthe tubular body while performing work as a double acting or as singleacting cylinder with capability to retract by its own vacuum force.Because of experimental findings cited, identifying clearly that the useof U-cups in lieu of 0- rings not only simplifies such assembly but alsoeliminates the need to control piston air lock and the use of doubleseals in-many applications, in particular in such applications that cantolerate their use, U-cups were chosen. Specifically, the U-cups areconsidered low pressure seals, and therefore their use may be associatedwith power cylinders serving such pressu-re ranges. However some designsof U-cups can be used for high pressures as well.

Shown in FIG. 2 is an all-plastic one piece molded cylinder housing 40having a tubular body 60 of differential internal diameters with openreceiver end 44 of enlarged cylindrical diameter 55 at one cylinder endand a closed opposite end 32 with integrally molded blind end wall 54 atthe end of a smaller coaxial cylindrical portion 34, initiating midwaywith shoulder 38 acting as a stop for larger diameter piston in service.

A fluid entrance port 37 is provided in the cylinder blind end wall 54to serve as fluid supply and exhaust port means when provided with a3-way directional operating valve (not shown).

An all-plastic one piece molded piston and rod assembly 56 with anelongated differential diameter piston 52 at one end and a solid pistonrod 49 at the other opposite end has a short larger diameter piston 43situated midway and terminating with a raiser 43 having coaxiallyattached by molding piston rod 49, and a shoulder 36 on the pistoninside. I

With the cylinder receiver end 44 open, the piston and rod assembly 56is slidably inserted into cylinder 60 by having elongated piston 52 toenter smaller cylindrical portion 34 and larger short piston 43 to enterenlarged cylindrical portion 55 until shoulder 36 of piston 43 bottomsshoulder 38 of cylinder 60 displacing air therefrom when assembly iscompleted and comprising the first piston rod retracted position incylinder operation before the working fluid entering via port 37 beginsto act over the piston rod end 51. The diameters of pistons 52 and 43are made to be slightly less than their respective cylindrical portionsto facilitate close sliding fit of piston and rod assembly 56 insidetubular body 60. A rod end closure 47 provided with central opening 48for the passage of piston rod 49 is slipped over and securedin thereceiver open end by way of threads 46 permanently serving as a stopagainst the inside face 50 defining stroke to completethis assembly. Thecentral opening 48 with piston rod 49 slidably assembled therethroughserves also as the bearing means for improved capability of thiscylinder tosustain side loads in operation. An annular space-63 of thepiston rod 49 inside opening 48 permits air venting during the pistonforward motion axially within its stroke limitation from the firstinitially assembled position with piston resting onshoulder of thecylinder as shown in FIG. 1 to that-of piston rod extended position asshown in FIG. 2 after the cylinder was energized by the working A fluidentering port 37 to act against piston end 51 creating such forwardmotion and forming void 39 in the cylinder end as shown in FIG. 2.Piston forward motion from the original assembly position creates alsoevacuated annulus 31 between the elongated smaller diameterpiston 52 andcylinder 55, as well as shoulder 36 of large diameter piston 43 andcylinder shoulder 38 separated by seals and 45 in their respectivegrooves 33 and 62. The annulus 31 under vacuum provides means forpistonreturn to the original assembly position together with atmosphericpressure action over larger diameter piston side with face raiser 53always exposed to the atmospheric air by way of annulus 63 shown, fa-

cilitating piston rod return from the second extended to first retractedposition by its own vacuum force as soon as the cylinder void 39 becomesopen to exhaust. And in turn, as soon as the cylinder void becomesreenergized, the position changes to that shown in FIG. 2 clearlyindentifying advantages of U-cup seal with mouth facing piston end 51which together with seal never leaves cylindrical piston 34 during theoperation of cylinder, and U-cup lip 61 resisting pressure leakage intoevacuated annulus 31 with pressure increase which also increases sealingabilities ofthe lip 61 against the wall of the smaller diameter cylinder34. Creation of vacuum when pressure enters cylinder end void 39 ishereby insured, although the cylinder operation and piston return by itsown vacuum force is attainable even without pressurization, asexperienced during the prototype tests after assemblying the piston rodwith U-cups inside the differential diameter cylinder of this designpositively displacing all air by flowing it across the seals with easefrom within the annulus 31 initially, and operating thereafter mannuallywhen pulled by protruding rod'extension with automatic return from thesecond piston extended to the first piston retracted position inaccordance with invention objectives disclosed.

For prevention of undesired dimensional changes of masses not properlyproportioned, in order to facilitate ability of cylinder manufacture bymolding, the cylinder components of FIG. 2 were modified in accordancewith molding requirements. Including in FIG. 2 is a recess 41 enteringradially cylinder blind end wall 54 to enable removal of cylinder corewithout undesirable radius and to insure cylinder manufacture withstraight tubular sections without undue stress raisers that in servicewill effect cylinder integrity. Also shown is an elongated blind cavity42 entering piston end 51 in-' wardly to terminate in the vicinity ofthe short larger diameter piston of this coaxial piston of differentialdiameters.

Thus it has been demonstrated that the differential diameter powercylinder with piston return by its own vacuum force as described aboveaccomplishes all stated objectives and provides drastically new'productof this type. y

Although a preferred embodiment of this invention is disclosed, it is tobe understood that various modifications and rearrangements of parts maybe resorted to without 'departingfrom the scope of thisinventiondisclosed and claimed herein.

What is claimed is: 1. A hydraulic/pneumatic power cylinder for use withpressurized working fluid comprising: I an elongated cylinder of tubularconfiguration, internally having a portion of smaller diameter with anend wall at one cylinder end forming one cylinder end blind, a shoulderapproximately midway leading to another coaxial portion of largerdiameter with an open end forming an opposite cylinder receiver end openand adaptable to be closed by a rod end closure, a fluid supplyv andexhaust port means in said cylinder. blind end, a rod end closureincluding a central opening and mounted on said open end a coaxialpiston and rod assembly with a differential diameter piston having asmall diameter elongated piston at one end and a piston rod at the otherend with a larger diameter short piston approximately midway thereof,said small elongated piston being in close sliding fit with said smallerdiameter cylinder, said larger diameter short piston being in closesliding fit said larger cylinder, said piston rod'being permanentlysecured to the face of said larger diameter piston centrally comprisinga coaxial piston and rod assembly, said piston being slidably receivedin said elongated cylinder with the small diameter elongated pistonentering the small diameter cylinder and the larger diameter shortpiston entering the larger diameter cylinder until it abuts and bottomsat said shoulder, seals on said small piston exposed to said cylinderblind end and on said larger diameter short piston, said piston rodprotruding said cylinder open end when said larger diameter short pistonis bottomed at said shoulder, said rod closure slidably accommodatingsaid pis-ton rod, fastening means for securing said rod end closurewithin said cylinder open receiver end to close said cylinder and toserve as a piston stop when the piston is urged to axially move from afirst piston rod retracted position toa se-cond piston rod extendedposition, venting means for admitting atmospheric pressure to the spacebetween said larger piston and said rod end closure, said small andlarger piston, said seals, said cylinder, and said shoulder defining anisolated and evacuated annulus when said piston rod is moved to extendaxially therein to assume said second piston rod extended position,whereby a vacuum'force is generated which force together withatmospheric pressure acting over the surface of larger piston and rodexposed thereto develops a sufficiently large combined force for pistonrod return by its own vacuum force from the second piston rod extendedposition to the first piston rod retracted position, and whereby whensaid piston is in said piston rod extended position, said small pistonend with said seal is engaged in said smaller diameter cylinder portion.r

2. A hydraulic/pneumatic power cylinder for use with pressurized workingfluid comprising:

an elongated cylinder of tubular configuration internally having aportion of smaller diameter with an end wall at one cylinder end formingone cylinder end blind, a shoulder approximately midway leading toanother coaxial portion of larger diameter with anopen end forming anopposiee cylinder receiver end open and adaptable to be closed by a rodend closure,

a fluid. supply and exhaust port means in said cylinder blind end,

a coaxial piston and rod assembly with small and large diameter pistonsincorporated therein having .a small diameter elongated piston at oneend and a piston rod at the other end with a larger diameter shortpiston approximately midway thereof, said small elongated piston beingin close sliding fit with said small diameter cylinder, and said largerdiameter short piston being in close sliding fit with said largercylinder,

saidpiston rod permanently secured to the face of said larger diameterpiston and located centrally to provide said coaxial piston and rodassembly, seals on said small and large pistons, said piston slidablyreceived in said cylinder with the small diameter elongated pistonentering the small diameter cylinder and the larger short diameterpiston entering larger diameter cylinder for operating between a firstpiston rod'retracted position and a second piston rod extended position,whereby when said piston is in the first retracted position, said largerdiameter short piston abuts and bottoms said shoul der while saidelongated small piston fully engages the small diameter cylinder portionthereby displacing all air from the space occupied by said piston, andwhen said piston is in the second extended position, an isolated andevacuated annulus is created between said smaller and larger pistons,said seals, said cylinder, and said shoulder when said larger pistonmoves axially away from said shoulder upon cylinder actuation bypressurized fluid entering fluid supply port means in said cylinderblind end, said evacuated annulus providing a vacuum force for pistonreturn to the original first piston rod retracted position automaticallywhen said pressurized fluid is allowed to escape from said cylinderblind end via said fluid exhaust port means,

rod receiving end closure secured in said cylinder open end includingventing means for the space between the larger piston and the end endclosure whereby when said short piston is moved from said first pistonrod retracted position to said second piston rod extended positionatmospheric air is displaced therefrom to facilitate proper operation ofthe cylinder and whereby when the cylinder blind end is allowed toexhaust, said atmospheric air returns thereto to act upon said largerdiameter short piston and together with said vacuum force in saidannulus to return said piston automatically to the original first pistonrod retracted position, said second piston rod extended position beingdetermined by the position of said rod end closure,

3. A cylinder as in claim 2 wherein said seals on said pistons are ofU-cup configuration.

4. A cylinder as in claim 1 wherein said small piston end includes dualseals with seal venting means therebetween for exhaust to theatmosphere, said seal venting means includinga passage initiatingbetween said seals of said elongated smalll piston end by enteringthereto radially to meet an axial passage provided therein communicationwith a passage in said piston rod leading to the atmosphere.

5. A cylinder as in claim 2 wherein all components are non-metallic.

6. A power cylinder with piston return by its own vacuum forcecomprising: a cylinder having shoulder defined between differentialdiameter portions, a piston having a shoulder defined betweendifferential diame- Q I ter portions, said piston in its retractedposition being positioned within said cylinder with said respectivedifferential diameter portions of said piston and cylinder being inclose sliding fit and with the respective shoulders of said piston andcylinder abutting and bottoming on one another, seals on thedifferential diameter portions of said piston, a piston rod attached tothe face of the larger diameter portion of saidipiston and protruding atone cylinder open end, a cylinder closure at another cylinder endadjacent said small dianieter comprising a cylinder blind end, portmeans opening into a said cylinder at said blind end for supply andexhaust of the pressurized working fluid and adaptable for connecting a3-way operating valve thereto to control the directional flow to andfrom the cylinder blind end during the cylinder operation, said cylinderoperation including piston axial movement from a first piston rodretracted position to a second piston rod extended position in responseto the directional flow of pressurized fluid whereby when said fluid isallowed to enter said cylinder blind end via said port provided therein,said piston is moved to assume said second piston rod extended position,and when said fluid is allowed to exhaust therefrom via said port, saidpiston is moved to assume said first piston rod retracted position, saidpiston motion from said first to said second positions developing anisolated and evacuated annulus between said piston and cylinder, saidseals. and said shoulders to produce a vacuum force large enough toreturn said 3 ,8 1 5,481 9 10 piston from said second to said firstpositions when said ing fit, and end face of the larger piston abuttingcylinder blind end is open to exhaust. and bottoming on said shoulder,and the larger pis- 7. A power cylinder with piston re by O n tonentering the larger diameter cylinder postion in force p close slidingfit for axial movement within the cylan elongated cylinder means havingone cylinder end blind defined by an end wall and another cylinder endopen, a rod end closure including a central opening connected bysecurement means to said open end, said cylinder means includinginternal diameter tubular portions of different coaxial diinder limitedby said rod end closure at one piston rod extended position and saidcylinder shoulder seals on said smaller and larger diameter pistonportions, said rod end closure opening receives said piston rod, fluidsupply and exhaust means at said irl nd,heb 'ct' n ameters separated bya shoulder substantially mid- Cy! b md er y f by pressurized workingfluid entering said fluld supply way thereof with the larger diameterportion mitld h t t m n id t m n ating at the cylinder open end whilethe smaller diaus por d if S i 5 mo.ves ameter portion continuesinwardly from said shoultowar S an exten e posmon eve g an def until itmeets Said blind end wall, 15 lated and evacuated annulus between saidshoulaplastic differential diameter piston means including Plston andcylmder pQrtlonsr and 531d a coaxial piston rod attached thereto, saidpiston seals {p t herem wherfiby p?" means having an elongated smallerdiameter piston exhaustmg Pressurlzed worklng fl through 51nd at one endand a short diameter larger piston with pp y and eXhaUSI f d piston eansIS resaid rod at the other end slidably received inside turned toretracted. PO t y e fOrCe of he said cylinder means with the smallpiston entering vacuum. the smaller diameter cylinder portion in closeslid-

1. A hydraulic/pneumatic power cylinder for use with pressurized workingfluid comprising: an elongated cylinder of tubular configuration,internally having a portion of smaller diameter with an end wall at onecylinder end forming one cylinder end blind, a shoulder approximatelymidway leading to another coaxial portion of larger diameter with anopen end forming an opposite cylinder receiver end open and adaptable tobe closed by a rod end closure, a fluid supply and exhaust port means insaid cylinder blind end, a rod end closure including a central openingand mounted on said open end a coaxial piston and rod assembly with adifferential diameter piston having a small diameter elongated piston atone end and a piston rod at the other end with a larger diameter shortpiston approximately midway thereof, said small elongated piston beingin close sliding fit with said smaller diameter cylinder, said largerdiameter short piston being in close sliding fit said larger cylinder,said piston rod being permanently secured to the face of said largerdiameter piston centrally comprising a coaxial piston and rod assembly,said piston being slidably received in said elongated cylinder with thesmall diameter elongated piston entering the small diameter cylinder andthe larger diameter short piston entering the larger diameter cylinderuntil it abuts and bottoms at said shoulder, seals on said small pistonexposed to said cylinder blind end and on said larger diameter shortpiston, said piston rod protruding said cylinder open end when saidlarger diameter short piston is bottomed at said shoulder, said rodclosure slidably accommodating said pis-ton rod, fastening means forsecuring said rod end closure within said cylinder open receiver end toclose said cylinder and to serve as a piston stop when the piston isurged to axially move from a first piston rod retracted position to ase-cond piston rod extended position, venting means for admittingatmospheric pressure to the space between said larger piston and saidrod end closure, said small and larger piston, said seals, saidcylinder, and said shoulder defining an isolated and evacuated annuluswhen said piston rod is moved to extend axially therein to assume saidsecond piston rod extended position, whereby a vacuum force is generatedwhich force together with atmospheric pressure acting over the surfaceof larger piston and rod exposed thereto develops a sufficiently largecombined force for piston rod return by its own vacuum force from thesecond piston rod extended position to the first piston rod retractedposition, and whereby when said piston is in said piston rod extendedposition, said small piston end with said seal is engaged in saidsmaller diameter cylinder portion.
 2. A hydraulic/pneumatic powercylinder for use with pressurized working fluid comprising: an elongatedcylinder of tubular configuration internally having a portion of smallerdiameter with an end wall at one cylinder end forming one cylinder endblind, a shoulder approximately midway leading to another coaxialportion of larger diameter with an open end forming an opposiee cylinderreceiver end open and adaptable to be closed by a rod end closure, afluid supply and exhaust port means in said cylinder blind end, acoaxial piston and rod assembly with small and large diameter pistonsincorporated therein having a small diameter elongated piston at one endand a piston rod at the other end with a larger diameter short pistonapproximately midway thereof, said small elongated piston being in closesliding fit with said small diameter cylinder, and said larger diametershort piston being in close sliding fit with said larger cylinder, saidpiston rod permanently secured to the face of said larger diameterpiston and located centrally to provide said coaxial piston and rodassembly, seals on said small and large pistons, said piston slidablyreceived in said cylinder with the small diameter elongated pistonentering the small diameter cylinder and the larger short diameterpiston entering larger diameter cylinder for operating between a firstpiston rod retracted position and a second piston rod extended position,whereby when said piston is in the first retracted position, said largerdiameter short piston abuts and bottoms said shoulder while saidelongated small piston fully engages the small diameter cylinder portionthereby displacing all air from the space occupied by said piston, andwhen said piston is in the second extended position, an isolated andevacuated annulus is created between said smaller and larger pistons,said seals, said cylinder, and said shoulder when said larger pistonmoves axially away from said shoulder upon cylinder actuation bypressurized fluid entering fluid supply port means in said cylinderblind end, said evacuated annulus providing a vacuum force for pistonreturn to the original first piston rod retracted position automaticallywhen said pressurized fluid is allowed to escape from said cylinderblind end via said fluid exhaust port means, a rod receiving end closuresecured in said cylinder open end including venting means for the spacebetween the larger piston and the end end closure whereby when saidshort piston is moved from said first piston rod retracted position tosaid second piston rod extended position atmospheric air is displacedtherefrom to facilitate proper operation of the cylinder and wherebywhen the cylinder blind end is allowed to exhaust, said atmospheric airreturns thereto to act upon said larger diameter short piston andtogether with said vacuum force in said annulus to return said pistonautomatically to the original first piston rod retracted position, saidsecond piston rod extended position being determined by the position ofsaid rod end closure.
 3. A cylinder as in claim 2 wherein said seals onsaid pistons are of U-cup configuration.
 4. A cylinder as in claim 1wherein said small piston end includes dual seals with seal ventingmeans therebetween for exhaust to the atmosphere, said seal ventingmeans including a passage initiating between said seals of saidelongated smalll piston end by entering thereto radially to meet anaxial passage provided therein communication with a passage in saidpiston rod leading to the atmosphere.
 5. A cylinder as in claim 2wherein all components are non-metallic.
 6. A power cylinder with pistonreturn by its own vacuum force comprising: a cylinder having shoulderdefined between differential diameter portions, a piston having ashoulder defined between differential diameter portions, said piston inits retracted position being positioned within said cylinder with saidrespective differential diameter portions of said piston and cylinderbeing in close sliding fit and with the respective shoulders of saidpiston and cylinder abutting and bottoming on one another, seals on thedifferential diameter portions of said piston, a piston rod attached tothe face of the larger diameter portion of said piston and protruding atone cylinder open end, a cylinder closure at another cylinder endadjacent said small diameter comprising a cylinder blind end, port meansopening into a said cylinder at said blind end for supply and exhaust ofthe pressurized working fluid and adaptable for connecting a 3-wayoperating valve thereto to control the directional flow to and from thecylinder blind end during the cylinder operation, said cylinderoperation including piston axial movement from a first piston rodretracted position to a second piston rod extended Position in responseto the directional flow of pressurized fluid whereby when said fluid isallowed to enter said cylinder blind end via said port provided therein,said piston is moved to assume said second piston rod extended position,and when said fluid is allowed to exhaust therefrom via said port, saidpiston is moved to assume said first piston rod retracted position, saidpiston motion from said first to said second positions developing anisolated and evacuated annulus between said piston and cylinder, saidseals, and said shoulders to produce a vacuum force large enough toreturn said piston from said second to said first positions when saidcylinder blind end is open to exhaust.
 7. A power cylinder with pistonreturn by own vacuum force comprising: an elongated cylinder meanshaving one cylinder end blind defined by an end wall and anothercylinder end open, a rod end closure including a central openingconnected by securement means to said open end, said cylinder meansincluding internal diameter tubular portions of different coaxialdiameters separated by a shoulder substantially midway thereof with thelarger diameter portion initiating at the cylinder open end while thesmaller diameter portion continues inwardly from said shoulder until itmeets said blind end wall, a plastic differential diameter piston meansincluding a coaxial piston rod attached thereto, said piston meanshaving an elongated smaller diameter piston at one end and a shortdiameter larger piston with said rod at the other end slidably receivedinside said cylinder means with the small piston entering the smallerdiameter cylinder portion in close sliding fit, and end face of thelarger piston abutting and bottoming on said shoulder, and the largerpiston entering the larger diameter cylinder postion in close slidingfit for axial movement within the cylinder limited by said rod endclosure at one piston rod extended position and said cylinder shoulderseals on said smaller and larger diameter piston portions, said rod endclosure opening receives said piston rod, fluid supply and exhaust meansat said cylinder blind end, whereby upon actuation by pressurizedworking fluid entering said fluid supply and exhaust port means saidpiston means moves towards an extended position developing an isolatedand evacuated annulus between said shoulder, said piston and cylinderportions, and said seals to produce a vacuum therein whereby uponexhausting pressurized working fluid through said supply and exhaustmeans said piston means is returned to a retracted position by the forceof he vacuum.